Printed electronics appear to hold a promise for enabling cost-effective integration of electronic functionality to a large variety of consumer products. Here it should be noted that even if a traditional, epoxy- or polyester based circuit board is often referred to as a printed circuit board (PCB), it does not fulfil the actual definition of printed electronics. In a PCB the use of (silk screen) printing is limited to producing the etch-resistant ink patterns prior to the etching of unwanted copper, as well as to producing visible markings on the surface of an otherwise completed board. True printed electronics mean that conductive, semiconductive and possibly other patterns that constitute actual functional elements of the electronic circuit are formed on a substrate in a printing process, i.e. printed on the substrate.
At the time of writing this description, the dimensions of typical printed electronics are macroscopic, at least compared to the micro- or nanometre scale line widths and other structures encountered in integrated circuits. This means that implementing complex functionalities with printed electronics requires using a relatively large surface area and/or augmenting the actual printed electronics with integrated circuit components or chips. Also the longer designation “semiconductor chip” can be used, but it should be noted that the base of a chip is not always made of semiconductor material: also e.g. glass-, sapphire-, and steel based chips are known, as well as chips printed with semiconductive polymers onto an isolating polymer base. If chips are to be used, there arises the natural need to attach and connect a chip to the printed electronics. In this description the term to attach and its derivatives mean attaching physically, i.e. keeping from coming loose, while the term to connect and its derivatives mean producing an electrically conductive connection. It should be noted, though, that these terms are not mutually exclusive, but a strong enough method like e.g. soldering may be used to simultaneously attach and connect.
FIG. 1 illustrates a known method for attaching and connecting a chip 101 to printed electronics, of which there are shown the conductive areas 102 and 103 that have been printed on a substrate 104. As an example, we may assume that the substrate 104 is paper or cardboard, and the conductive areas 102 and 103 are pieces of metallic foil (or more generally: areas covered with an essentially metallic compound). On the surface of the chip 101 are solder bumps 105 and 106, and corresponding patches of solder flux 107 and 108 have been spread on the conductive areas 102 and 103. The flux could also have been spread on the solder bumps 105 and 106, or provided in the material of the solder bumps. A drop of glue 109 has been applied to that surface of the chip 101 that faces the substrate 104. The glue helps to keep the chip immobilized at the desired location during the time when sufficient heat is applied to cause at least partial melting of the solder bumps. The flux helps to control the flowing of the melted solder. After cooling, the chip remains attached to the substrate, with electric connections established at the locations where the melting solder formed a bond with the appropriate parts of the conductive areas.
A disadvantage of the prior art method illustrated in FIG. 1 is that it is relatively slow. It is not uncommon that 10 to 15 seconds are needed to attach and connect a single chip. This may prove way too slow for example for large-scale manufacturing of cardboard-made consumer packages for food supplies.